The broad and long-term objective of this research project is to test the hypothesis that simultaneous sympathovagal discharges are the immediate triggers of paroxysmal atrial fibrillation (PAF) and that severing the connection between the autonomic nerves and the heart can reduce the incidence of PAF. Autonomic nervous system is thought to be important in mediating PAF. However, no studies have documented a direct relationship between autonomic nerve discharges and the mechanisms of PAF in ambulatory animals. The mechanisms by which autonomic nerve discharges trigger AF are also poorly understood. The research project is designed to accomplish the following specific aims: (1) We will perform long-term simultaneous recordings of electrocardiogram (ECG), blood pressure, right and left stellate ganglion nerve activity and cardiac vagal nerve activity in a canine model of spontaneous PAF induced by short-term rapid atrial pacing. The data will be used to test the hypothesis that simultaneous sympathovagal activation is the most common immediate trigger of PAF in ambulatory dogs. (2) We will perform high density mapping of pulmonary veins to test the hypothesis that repetitive rapid activities in these veins can be induced by stimulation of stellate ganglia and vagal nerves in this canine model of PAF. The results will be used to test the hypothesis that sympathovagal stimulation can induce focal discharges from the remodeled pulmonary veins characterized by an increased density of autonomic nerve endings. (3) We will perform cryoablation of the left stellate ganglion and cardiac vagal nerves in the same animal models of PAF as that described in Aim 1. We will then perform long-term simultaneous recordings of ECG, blood pressure and autonomic nerve activities. The results will be used to test the hypothesis that selective cardiac sympathetic and vagal denervation can significantly reduce the incidence of PAF. (4) We will perform simultaneous membrane potential and intracellular calcium mapping of canine pulmonary veins with or without norepinephrine and acetylcholine infusion. The results will be used to test the hypothesis simultaneous norepinephrine and acetylcholine stimulation in canine PV in vitro promotes triggered activity through Ca transient triggering mechanisms.